1. Field of the Invention
This invention relates to certain 4-aminomethyl-2-substituted imidazole and 2-aminomethyl-4-substituted derivatives which selectively bind to brain dopamine receptor subtypes. This invention also relates to pharmaceutical compositions comprising such compounds. It farther relates to the use of such compounds in treating affective disorders such as schizophrenia and depression as well as certain movement disorders such as Parkinsonism. Furthermore, compounds of this invention may be useful in treating the extrapyramidyl side effects associated with the use of conventional neuroleptic agents. The interaction of these aminomethylimidazole derivatives of the invention with dopamine receptor subtypes is described. This interaction results in the pharmacological activities of these compounds.
2. Description of the Related Art
Schizophrenia or psychosis is a term used to describe a group of illnesses of unknown origin which affect approximately 2.5 million people in the United States. These disorders of the brain are characterized by a variety of symptoms which are classified as positive symptoms (disordered thought, hallucinations and delusions) and negative symptoms (social withdrawal and unresponsiveness). These disorders have an age of onset in adolescence or early adulthood and persist for many years. The disorders tend to become more severe during the patient's lifetime and can result in prolonged institutionalization. In the United States today, approximately 40% of all hospitalized psychiatric patents suffer from schizophrenia.
During the 1950's physicians demonstrated that they could sucessfully treat psychotic patients with medications called neuroleptics; this classification of antipsychotic medication was based largely on the activating (neuroleptic) properties of the nervous system by these drugs. Subsequently, neuroleptic agents were shown to increase the concentrations of dopamine metabolites in the brain suggesting altered neuronal firing of the dopamine system. Additional evidence indicated that dopamine could increase the activity of adenylate cyclase in the corpus striatum, an effect reversed by neuroleptic agents. Thus, cumulative evidence from these and later experiments strongly suggested that the neurotransmitter dopamine was involved in schizophrenia.
One of the major actions of antipsychotic medication is the blockade of dopamine receptors in brain. Several dopamine systems appear to exist in the brain and at least five classes of dopamine receptors appear to mediate the actions of this transmitter. These dopamine receptors differ in their pharmacological specificity and were originally classified upon these differences in the pharmacology of different chemical series. Butyrophenones, containing many potent antipsychotic drugs were quite weak at the dopamine receptor that activated adenylate cyclase (now known as a D1 dopamine receptor). In contrast, they labelled other dopamine receptors (called D2 receptors) in the subnanomolar range and a third type D3 in the nanomolar range. Two additional receptor subtypes have also been identified. D5 which is somewhat similar to D1 receptor type and D4 which is closely related to D3 and D2 receptor types. Phenothiazines possess nanomolar affinity for all three types of dopamine receptors. Other drugs have been developed with great specificity for the D1 subtype receptor and for the D2 subtype receptor.
A certain group of drugs (such as sulphide and clozapine) have been developed with a lesser incidence of extrapyramidal side effects than classical neuroleptics. In addition, there is some indication that they may be more beneficial in treating negative symptoms in some patients. Drugs of this class are often referred to as atypical antipsychotic agents. Since all D2 blockers do not possess a similar profile, hypotheses underlying the differences have been investigated. The major differences have been in the anticholinergic actions of the neuroleptics as well as the possibility that the dopamine receptors may differ in motor areas from those in the limbic areas thought to mediate the antipsychotic responses. The existence of the D3, D4 and D5 and other as yet undiscovered dopamine receptors may contribute to this profile. Some of the atypical compounds possess similar activity at D2, D3 and D4 receptors. The examples of this patent fall into this general class of molecules.
Using molecular biological techniques it has been possible to clone cDNAs coding for each of the pharmacologically defined receptors. There are at least two forms of D1-type receptors which have been classified as D1 and D5, and two forms of D2-type receptors, classified now as D2 and D4 dopamine receptors. In addition, there is at least one form of D3 dopamine receptor. Examples from the substituted aminomethylimidazole series of this patent possess differential affinities for each receptor subtype.
Schizophrenia is characterized by a variety of cognitive dysfunctions; schizophrenic patients perform less well than other groups on most cognitive or attentional tasks. The positive and negative symptom dimensions of schizophrenia are also associated with distinct cognitive deficits. In general, positive symptoms (disordered thought processes, hallucinations and decisions) are related to auditory processing impairments including deficits in verbal memory and language comprehension. Negative symptoms (social withdrawal and unresponsiveness) are related more to visual/motor dysfunctions including poorer performance on visual memory, motor speed and dexterity tasks.
These disorders have an age of onset in adolescence or early adulthood and persist for many years. The interaction of frontal and septo-hippocampal brain systems, and failures of information processing and self monitoring have been theorized as the basis of positive symptoms. Negative symptoms are thought to arise from abnormalities in the interactions of frontal and striatal systems. Since cognitive disturbances are present in most of the patients diagnosed as having schizophrenia, it has been theorized that to understand the pathogenesis and etiology of schizophrenia one must understand the basic dysfunction of the cognitive disorder.
The cognitive disturbances found in schizophrenia include, but are not limited to, various verbal and visual memory deficits. There are various neurocognitive tasks for both animals and humans that have been developed to assess memory deficits, as well as memory enhancements, of various treatments. Many of the neurocognitive behavioral tasks are modulated or mediated by eural activity within the hippocampal brain system noted above.
Drug substances that interact with the hippocampus are capable of modulating memory in animals. Certain memory paradigms employed in animals have construct and predictive validity for memory assessment in humans. In animals (rodents), paradigms such as the Step-Down Passive Avoidance Task assay or the Spatial Water Maze Task assay reliably detect deficits produced by certain drugs in humans. For example, commonly prescribed benzodiazepine anxiolytics and sedative hypnotics are known to produce memory impairment in humans, including varying degrees of anterograde amnesia (depending on the exact drug). In the step-down passive avoidance paradigm, these very same drugs disrupt the memory of animals given the compounds during the information acquisition or processing period. Likewise, benzodiazepines disrupt information processing and memories in the spatial water maze task in rodents. Thus, these animal models can be used to predict the memory impairing effects of certain compounds in humans. Conversely, these same animal models can predict the memory improving or enhancing effects of compounds in humans. Although fewer in number, drugs that improve memory in humans (e.g., Nootroprice, Beta carbolines) produce memory enhancing effects in rats in these models. Therefore, the spatial water maze and step-down passive avoidance paradigms in rodents are useful in predicting memory impairing and memory enhancing effects of test compounds in humans.